Because the domain name is not necessarily a strong factor for ranking all on its own. In fact, depending on the word in the domain name, if it is considered a "keyword exact match" domain name (as opposed to a brand name) it may even hurt you in search visibility.

The domain name term on its own is likely more competitive than longer phrases ("example" + another keyword), which means it's going to be harder to achieve visibility for that search term. Simply having that term as your domain name is not going to get the job done.

Compared to the pages that do show for "example," how old is your site? Compared to the sites those pages live on, how many pages do they have, compared to yours? How much content do they contain compared to yours?

Compared to the pages that show for "example," how does the quality of the content of your home page compare? Assuming these other pages have been online longer than yours, would an objective third-party observer consider your content to be at least two or three times better than the others? Is it more interesting, better written, more useful?

What sort of external links do you have pointing to the pages of your site? Do they all point to the home page, or are link targets spread throughout the pages of your site? Are the external links primarily (or all) links you "built" yourself(1) or are a good percentage of them earned editorial links(2)?